Asphaltene self-association and precipitation are unfavorable processes that can occur during production, transportation, and storage of crude oils. The primary mechanisms of asphaltene self-association are dispersion interactions, electrostatics interactions, hydrogen bonding, and orientation-dependent repulsive steric interactions. This process consists of sequential steps initiating with nano-aggregation of five to six asphaltene molecules and continues by increasing its concentration into formation of clusters. Further augmentation of asphaltene dosage leads to formation of asphaltene micro-aggregates that are detrimental to oil rheological behavior. However, a more detailed and comprehensive interpretation is required to determine the contribution of each mechanism in aforementioned steps.
In the present work, asphaltene samples from a light crude oil have been accordingly fractionated by various precipitants and analyzes chemically in various solvents by none-fragmenting techniques such as matrix-assisted laser desorption/ionization (MALDI). Influences of heteroatoms on asphaltene precipitation mechanisms and molecular weight were assessed by conducting elemental analysis. Sensitivity of asphaltene constituents stacking to extraction methods were evaluated by curve deconvolution and fitting routines of X-ray diffraction (XRD) patterns of solid asphaltenes. Finally, asphaltene precipitation onsets were determined for various asphaltene samples and conditions by using near-infrared (NIR) spectroscopy technique.
Results of the current study reveal the substantial impacts of various precipitants and solvents on asphaltene aromaticity and its propensity toward self-association. Also, the results indicate that alteration of the extraction methods is conducive to variation in asphaltene molecular weights as well as precipitation onset points. Alteration of critical aggregate concentration (CAC) and critical micelle concentration (CMC) were observed from NIR results and were used to determine asphaltene stability.
Current study proposes further understanding of asphaltene self-association and aggregation mechanisms. Concrete understanding of these mechanisms leads to designing more efficient asphaltene dispersants and heavy oil viscosity modifiers to prompt higher oil recovery and facilitate transportation processes.